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United States Patent |
5,048,607
|
Phelps
,   et al.
|
September 17, 1991
|
In-situ emulsion polymerization of ethylene derivatives
Abstract
A profile control method for closing off a more permeable zone of a
formation where water, high fluid flow, or high perssures are encountered.
A water-external emulsion containing a monomer, a cross-linker, free
radical initiators and reaction inhibitors is injected into the formation.
There they react to form plastic-like solid spheres in the more permeable
formation zone. Because the spheres are not water soluble and have high
compressive strength, they can be used in severe flow applications.
Ethylene, propylene and styrene monomers can be utilized to form solid
spheres of polyethylene, polypropylene or polystyrene.
Inventors:
|
Phelps; Craig H. (Bakersfield, CA);
Strom; E. Thomas (Dallas, TX);
Hoefner; Mark L. (Dallas, TX)
|
Assignee:
|
Mobil Oil Corporation (Fairfax, VA)
|
Appl. No.:
|
565596 |
Filed:
|
August 10, 1990 |
Current U.S. Class: |
166/270; 166/281; 166/295; 523/130 |
Intern'l Class: |
E21B 033/138; E21B 043/22 |
Field of Search: |
166/281,288,270,295,300,272,273,274
523/130
|
References Cited
U.S. Patent Documents
2402588 | Jun., 1946 | Andresen.
| |
3490533 | Jan., 1970 | McLaughlin | 166/270.
|
3645336 | Feb., 1972 | Young et al. | 166/288.
|
3805893 | Apr., 1974 | Sarem | 166/270.
|
3965986 | Jun., 1976 | Christopher | 166/292.
|
4168614 | Sep., 1979 | Rieuz | 166/295.
|
4458760 | Jul., 1984 | Hurd | 166/273.
|
4676318 | Jun., 1987 | Myers et al. | 166/293.
|
4804043 | Feb., 1989 | Shu et al. | 166/263.
|
4830108 | May., 1989 | Hazlett et al. | 166/270.
|
4844163 | Jul., 1989 | Hazlett et al. | 166/300.
|
4951921 | Aug., 1990 | Stahl et al. | 166/274.
|
Primary Examiner: Suchfield; George A.
Attorney, Agent or Firm: McKillop; Alexander J., Speciale; Charles J., Malone; Charles A.
Claims
What is claimed:
1. A method for profile control in a subterranean hydrocarbonaceous
fluid-containing formation or reservoir where substantially high flow
rates or high pressures are encountered comprising:
a) injecting into a more permeable zone of said formation a water-external
emulsion which contains an ethylene monomer derivative and a cross-linker
in an amount sufficient to form plastic-like solid spheres; and
b) allowing said emulsion to remain in the more permeable zone for a time
sufficient to form in-situ plastic-like solid spheres by polymerization
therein which spheres are sufficient to divert fluids utilized in enhanced
oil recovery operations from said zone where high flow rates and high
pressures are encountered.
2. The method as recited in claim 1 where the ethylene derivative comprises
styrene and the cross-linker comprises divinylbenzene.
3. The method as recited in claim 1 where a surfactant, a free radical
initiator, and a retarder are utilized.
4. The method as recited in claim 1 where fluids precluded from entry into
said more permeable zone of a formation include steam, hydrocarbons,
water, carbon dioxide, alkaline flooding agents, nitrogen gas,
surfactants, foam, acids, or polymers.
5. The method as recited in claim 1 where the ethylene derivative comprises
poly-3-methyl-1-butene, poly-4,4-dimethyl-1-butene,
poly-ortho-methylstyrene, or poly-4,4-dimethyl-1-pentene and mixtures
thereof.
6. The method as recited in claim 1 where the ethylene derivative comprises
ethylene, propylene, and styrene monomers which subsequently form solids
of polyethylene, polypropylene, or polystyrene.
7. The method as recited in claim 1 where a substantially bimodal
distribution of plastic-like solid spheres is obtained upon polymerization
within said formation.
8. The method as recited in claim 1 where polymerization is controlled by
varying a ratio of free radical initiator to retarder contained in the
emulsion which controls the distance at which the spheres are formed in
said formation.
9. The method as recited in claim 1 where a substantially bimodal
distribution of spheres is obtained wherein smaller spheres are capable of
plugging pore throats in a formation while larger spheres will plug pores
and fractures within a formation.
10. The method as recited in claim 1 where injection of the emulsion is
accompanied by a pumping action which provides agitation that keeps said
emulsion stable while polymerization takes place.
11. The method as recited in claim 1 where a carbon dioxide or waterflood
enhanced oil recovery method is used to remove hydrocarbonaceous fluids
from a zone of lesser permeability after step b).
12. The method as recited in claim 1 where in step a) the fracturing
pressure of the formation is not exceeded when said emulsion is injected
into the more permeable zone.
13. A method for profile control in a subterranean hydrocarbonaceous
fluid-containing formation or reservoir where substantially high flow
rates or high pressures are encountered comprising:
a) injecting a prepad of sacrificial brine into a more permeable zone of
said formation so that a surfactant contained in a water-external emulsion
will not be absorbed on rock surfaces in said permeable zone;
b) injecting via a pumping action the water-external emulsion which
additionally contains an ethylene monomer derivative and a cross-linker in
an amount sufficient to form plastic-like solid spheres; and
c) allowing said emulsion to remain in the more permeable zone for a time
sufficient to form in-situ plastic-like solid spheres by polymerization
therein which spheres are sufficient to divert fluids utilized in enhanced
oil recovery operations from said zone where high flow rates and high
pressures are encountered.
14. The method as recited in claim 13 where the ethylene derivative
comprises styrene and the cross-linker comprises divinylbenzene.
15. The method as recited in claim 13 where a free radical initiator and a
retarder are utilized.
16. The method as recited in claim 13 where fluids precluded from entry
into said more permeable zone of a formation include steam, hydrocarbons,
water, carbon dioxide, alkaline flooding agents, nitrogen gas,
surfactants, foam, acids, or polymers.
17. The method as recited in claim 13 where the ethylene derivative
comprises poly-3-methyl-1-butene, poly-4,4-dimethyl-1-butene,
poly-ortho-methylstyrene, or poly-4,4-dimethyl-1-pentene and mixtures
thereof.
18. The method as recited in claim 13 where the ethylene derivative
comprises ethylene, propylene, and styrene monomers which subsequently
form solids of polyethylene, polypropylene, or polystyrene.
19. The method as recited in claim 13 where a substantially bimodal
distribution of plastic-like solid spheres is obtained upon polymerization
within said formation.
20. The method as recited in claim 13 where polymerization is controlled by
varying a ratio of free radical initiator to retarder contained in the
emulsion which controls the distance at which the spheres are formed in
said formation.
21. The method as recited in claim 13 where a substantially bimodal
distribution of spheres is obtained wherein smaller spheres are capable of
plugging pore throats in a formation while larger spheres will plug pores
and fractures within a formation.
22. The method as recited in claim 13 where said pumping action provides
agitation that keeps said emulsion stable while polymerization takes
place.
23. The method as recited in claim 13 where a carbon dioxide or waterflood
enhanced oil recovery method is used to remove hydrocarbonaceous fluids
from a zone of lesser permeability after step c).
24. The method as recited in claim 13 where in step b) the fracturing
pressure of the formation is not exceeded when said emulsion is injected
into the more permeable zone.
Description
FIELD OF THE INVENTION
This invention relates to a method for reducing permeability of a
subterranean formation. Primarily it is for use in a formation where
water, high fluid flow, or high pressures are encountered. More
particularly, this invention relates to a method for blocking an area of a
subterranean formation by the use of a plastic-like solid.
BACKGROUND OF THE INVENTION
Various methods have been proposed so that injected fluids can be diverted
to uncontacted zones of a reservoir. One such method is disclosed in U.S.
Pat. No. 2,402,588 issued to Andresen. This patent discloses a method of
sealing a more permeable area of the reservoir by injecting into a
reservoir a dilute alkaline solution of sodium silicate under low
pressure. An acid gas such as carbon dioxide is then injected to reduce
the alkalinity of the solution, resulting in gelling.
Another method is disclosed in U.S. Pat. No. 3,645,336 issued to Young et
al. This patent teaches the plugging of a zone of a reservoir by injecting
a mixture of steam and sodium silicate into the permeable zone. A second
mixture containing steam and a gelling agent such as carbon dioxide is
injected into the permeable zone, and the two mixtures are allowed to
react. A hard silica gel plug is formed.
Yet another method is disclosed in U.S. Pat. No. 3,805,893 which issued to
Sarem. Sarem discloses the formation of a gelatinous precipitate by
injection of small slugs of dilute aqueous alkaline metal silicate
solution, followed by water and then a dilute aqueous solution of a water
soluble material which reacts with the alkali metal silicate to form a
precipitate. The precipitate hardens to form a substantially impermeable
substance.
U.S. Pat. No. 3,965,986 issued to Christopher discloses still another
method. Here, a slug of fumed colloidal silica and water is injected into
a reservoir. This slug has a relatively low viscosity. A surfactant is
then injected which forms a gel on contact with the silica slug.
Meyers et al. disclosed a method for reducing the permeability of a
subterranean formation in U.S. Pat. No. 4,676,318. Here, an alkali metal
silicate was produced by injecting into the formation a solution of alkali
metal silicate and a chemical surfactant, along with a non-condensible
gas. The foam hardens into a substantially impermeable solid. The foam may
be used to reduce permeability in areas of the formation which have been
steam swept during steam stimulation cycles. Thus, subsequent steam
stimulation cycles were directed to uncontacted areas of the formation.
Many of the materials proposed for profile control of injected or produced
fluids have been polymer hydrogels. These gels are formed either in-situ
or ex-situ by blending 100 to 10,000 ppm of a water soluble polymer with
an appropriate cross-linker. These types of gels are advantageous in many
situations because their dilute polymer concentration makes them
relatively inexpensive. However, their water soluble nature and relatively
low elastic limits may render them inappropriate for profile control in
extremely high flow rate or high pressure applications such as a plugging
of a hydraulically-induced fracture.
Therefore, what is needed is a water-external component system which will
have a very high elastic limit or compressive strength so as to be able to
resist high pressure and high fluid flow within a formation.
SUMMARY OF THE INVENTION
In the practice of this invention, an emulsion is directed into a more
permeable zone of the formation. The emulsion comprises a polyethylene
derivative with a cross-linker therein along with initiators and retarders
which allows polymerization to take place in-situ. The polymerizable
components form a water-external emulsion. Upon polymerization, the
components react to form a plastic-like solid in a more permeable zone of
the formation due to heat contained in the formation. Because the solid is
not water-soluble and has high compressive strength, it can be used in
severe flow and high pressure applications where fluids such as water are
encountered. Because of a bimodal distribution of the plastic-like solid
spheres, said spheres can be used to plug pore throats within a formation
as well as a fracture within the formation. Ethylene derivatives
cross-linked with an appropriate cross-linker form the plastic-like solid
spheres. Monomers which can be utilized include ethylene, propylene, and
styrene, which are polymerized in-situ to form plastic-like solids of
polyethylene, polypropylene, or polystyrene. Fluids which can be diverted
by these materials include water, carbon dioxide, hydrocarbon gases,
gaseous nitrogen, steam, alkaline flooding agents, surfactants, foams,
polymers, and acids.
It is therefore an object of this invention to provide for a water-external
emulsion which can be used to form a plastic-like solid within a formation
to preclude fluid entry by most fluids used in enhanced oil recovery
methods.
It is another object of this invention to provide for a method whereby the
formulation of a water-external emulsion can be modified and injected into
a formation, thus allowing for variable propagation distances prior to
forming a plastic-like solid.
It is yet another object of this invention to provide for the formation of
a plastic-like solid material by polymerization in-situ at temperatures
existing within a reservoir.
It is yet another object of this invention to polymerize ethylene
derivatives in an oil-bearing formation so as to redirect fluids flowing
at high pressures and high rates such as occur in some
hydraulically-induced fractures.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graphical illustration of the particle size distribution of the
polystyrene spheres.
FIG. 2 is a graphical illustration of the particle size distribution of the
polystyrene spheres and the cumulative volume percent for the various
particle sizes.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In flooding operations, a fluid, usually water, is injected into the
subterranean, oil-bearing formation through an injection well which
extends from the surface of the earth down into a formation. A production
well also extends into the formation at an offset or horizontal distance
from the injection well so that, as the flooding liquid is injected into
the formation through the injection well, it displaces the oil towards the
production well. The oil is subsequently recovered from the production
well. Once the oil has been displaced from a swept zone of the formation,
an unswept zone may remain which contains additional oil. Often, more than
one injection well and more than one production well will be used in order
to cover the field adequately and maximize recovery. Various arrangements
of injection and production wells are used to this end, e.g., linear
arrangements to form a line drive, five spot, inverted five spot, seven
spot, inverted seven spot, all of which are established in conventional
practice.
To remove oil or hydrocarbonaceous fluids remaining in an unswept zone, a
non-water soluble emulsion containing a monomer, a cross-linker, reaction
initiators, and reaction inhibitors, is injected into a swept zone of the
formation. After entering the formation, the monomer forms a plastic-like
solid sphere upon cross-linking at temperatures existing in the formation
through a polymerization process. Since the solid is not water soluble and
has a high compressive strength, it can be used in severe flow and high
pressure applications. Ethylene, propylene and styrene monomers can be
utilized to form solids of polyethylene, polypropylene or polystyrene.
Prior to injecting the water-external or oil-in-water emulsion containing a
monomer and a cross-linker, a prepad of sacrificial brine is pumped into
the formation. The brine saturates at adsorption sites on rock surfaces so
that a surfactant contained in the emulsion will not be adsorbed. Pumping
action during the injection of the emulsion into the formation provides
the necessary agitation which keeps the emulsion stable while the
polymerization process takes place. The water-external emulsion is formed
above ground under batch-wise conditions.
The emulsion which is formed can be tailored to fit varying formation
conditions so as to be properly utilized to resist the flow of various
types of fluids, i.e., steam, hydrocarbons, water, carbon dioxide,
alkaline flooding agents, nitrogen gas, surfactants, foam, acids or
polymers. As will be apparent to those skilled in the art, other fluids
commonly used in enhanced oil recovery can be utilized herein.
When pumping the emulsion into the formation, it is desired to have a
pressure and agitation rate sufficiently high to keep the emulsion
properly suspended until polymerization can occur. It is desirable in many
cases that the fracturing pressure of the formation or reservoir should
not be exceeded during injection. A process for the selective placement of
polymer gels for profile control in thermal oil recovery is discussed in
U.S. Pat. No. 4,804,043 which issued to Shu et al. on Feb. 14, 1989. This
patent is hereby incorporated by reference herein.
Although other ethylene derivatives have been mentioned, the preferred
monomer for utilization herein is styrene. Styrene and divinylbenzene are
emulsified with the surfactant so that the reaction can be carried out in
those formations where water is encountered. The emulsion proceeds into
the formation at temperatures existing therein after being injected into
the formation. Once polymerization has occurred at the temperatures
existing in the formation, plastic-like solid spheres are formed, thereby
blocking pores and any existing fractures within a more permeable zone of
the formation.
Although styrene is the preferred monomer, this process can be tailored to
fit varying formation conditions, depending upon the nature of the fluids
encountered, e.g., steam, hydrocarbons, water, carbon dioxide, alkaline
flooding agents, nitrogen gas, surfactants, foam, acids or polymers.
Should it be necessary to withstand higher temperatures, then polyethylene
derivatives such as poly-3-methyl-1-butene, poly-4,4-dimethyl-1-butene,
poly-ortho-methylstyrene, or poly-4,4-dimethyl-1-pentene may be
substituted. These polyethylene derivatives have a melting point of
310.degree. C., 350.degree. C., 360.degree. C., or 380.degree. C.
respectively. If milder conditions are encountered, then other
polyethylene derivatives may be used as will be recognized by those
skilled in the art.
Flexibility to vary placement of the water-external emulsion within the
formation before polymerization takes place is obtained by adding a
polymerization retarder such as, for example, potassium ferricyanide. By
varying the ratio of a free radical initiator to a retarder, the timing of
the polymerization reaction can be controlled, as well as the distance to
which the emulsion may travel before forming plastic-like solid spheres.
The following example illustrates how the polymerization reaction works.
EXAMPLE
A solution is made up of 2.5 grams of sodium dodecylsulfate, a surfactant.
It is placed into 90 grams of water within a 250 ml beaker. The solution
is purged with nitrogen for 15 minutes. Thereafter, 0.4 grams of sodium
persulfate, a free radical initiator, is added into 10 grams of water.
Next, 40 grams of styrene and 10 grams of divinylbenzene are added into
the water. The mixture is stirred and purged with nitrogen for 5 minutes
more. Stirring is continued and the temperature is raised to 65.degree. C.
In about an hour, a yellow emulsion is formed. The solution is stirred for
4 more hours. Afterwards, stirring is stopped. After the stirring is
stopped, the solution displayed a creamy color resultant from the
polystyrene spheres.
An analysis of particle size distribution was made with a Coulter counter.
This analysis showed a substantially bimodal distribution of polystyrene
spheres with a small amount of a third population in the 25-40 micron
range. This distribution is further amplified in the drawings, FIGS. 1 and
2.
The bulk of the spheres were in the 0.1-1 micron and 5-10 micron ranges.
The smallest spheres are capable of plugging pore throats while the larger
spheres are capable of plugging pores and fractures. Polystyrene has a
melting point of 240.degree. C., while the cross-linked polystyrene which
was formed has an even higher melting point. The cross-linked polystyrene
system is capable of resisting steam fluid flow.
The emulsion mentioned herein can be utilized prior to commencing a carbon
dioxide flood during profile control. A carbon dioxide profile control
method is mentioned in U.S. Pat. No. 4,830,108 which issued to Hazlett et
al. on May 16, 1989. A waterflood method which can be used herein is
disclosed in U.S. Pat. No. 4,458,760 which issued to Hurd. Both patents
are hereby incorporated by reference herein. Although the high or more
permeable zone of a formation has been closed by the plastic-like solid
spheres, hydrocarbonaceous fluids still remain in an area of lesser
permeability. After closing the zone of greater permeability, any of the
above mentioned enhanced oil recovery methods, as well as others, can be
used to remove hydrocarbonaceous fluids from the zone of lesser
permeability.
Although the present invention has been described with preferred
embodiments, it is to be understood that modifications and variations may
be resorted to without departing from the spirit and scope of this
invention, as those skilled in the art will readily understand. Such
modifications and variations are considered to be within the purview and
scope of the appended claims.
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